The present invention is related to a technique for generating signals (will be referred to as “pulse-width modulation signals” hereinafter), the pulse widths of which have been set in response to a time sequence of a plurality of data.
Signal generating apparatus (PWM modulation circuits) which generate pulse-width modulation signals from a time sequence of digital-formatted data are suitably utilized in, for example, class-D amplifying apparatuses. JP-A-2006-54815 discloses the following technical idea: That is, in a pulse-width modulation signal, time points of both a front edge and a rear edge in each of pulses of the pulse-width modulation signal are controlled in response to 2 pieces of data, so that a time period (will be referred to as “pulse period” hereinafter) in which the pulses are arranged in the pulse-width modulation signal is made two times longer than a time length of a sampling period of data. Further, JP-A-2006-54815 describes such an arrangement that pulse-width modulation signals (w1(t) and w2(t)) of two systems which have an in-phase relation are generated in such a manner that 2 pieces of pulses equivalent to a difference between both the pulse-width modulation signals may have pulse widths in response to 2 pieces of data.
However, in any of the arrangements disclosed in JP-A-2006-54815, the modulating operations of 2 pieces of data are merely carried out every pulse period. As a result, there is such a restriction that the sampling period cannot be set to the time length shorter than a half of the pulse period.